A vehicular slide door apparatus includes a slide door which is movable between an open position and a closed position, and a drive device having a shaft which couples the slide door and an electric motor. When the motor is turned on, the slide door moves. The shaft is provided with a magnetic member which is sensed while the shaft is rotating by a sensor having a Hall element. This allows a direct determination of the shaft rotation so that such determination and successive determinations of the slide door movement become as accurate and precise as possible.